1. Field of the Invention
The invention relates to head restraints forming the upper portion of a vehicle seat backrest that may be deployed, for example, to a relatively-forward position in the event of a rear collision in order to increase vehicle occupant safety.
2. Background Art
The prior art teaches an automotive seat that includes a seat cushion, and a backrest pivotally mounted to the seat cushion so that the backrest may be reclined at a selected angle relative to the seat cushion for comfort. To improve seat comfort, a headrest is often defined on the upper portion of the backrest, for example, by supporting a cushion atop the backrest using a pair of posts that are slidably received in complementary guides defined in the upper portion of the backrest frame.
To reduce the likelihood of an undesirable over-extension of the occupant""s cervical vertebra in a rear collision, the prior art teaches pivoting the headrest about a pivot axis positioned somewhat vertically beneath the headrest to a relatively forward position within the vehicle in response to such a rear collision. In this manner, the distance which an occupant""s head must otherwise travel before being accelerated through contact with the headrest is reduced. For example, in U.S. Pat. No. 5,378,043, the headrest is pivoted relative to the seat backrest using a lever mechanism coupled to a pressure plate disposed within the backrest beneath its upholstery. When the pressure plate is actuated by occupant inertial forces during a rear collision, the upper portion of the backrest or the headrest-supporting guides pivot about a predetermined axis to bring the headrest to a forward position within the vehicle.
Co-pending U.S. patent application Ser. No. 09/938,416 filed Aug. 23, 2001, which is assigned to the assignee of the invention, alternatively teaches a xe2x80x9cclamshellxe2x80x9d headrest assembly that includes an angularly-fixed, rearward base portion rigidly mounted atop the backrest on a pair of downwardly-extending posts that are slidably received in the backrest frame. The clamshell headrest assembly further includes a forward, occupant-engaging or xe2x80x9ccontactxe2x80x9d portion that is pivotally mounted to the base portion along the base portion""s upper edge. A compression spring operates to bias the lower edge of the contact portion toward the seated occupant, while a spread-lever arrangement operated by a tensioned Bowden cable draws the lower edge of the contact portion back against the base portion. When the occupant exerts a threshold occupant inertial force against a pressure plate disposed within the backrest, the Bowden cable is released to permit the xe2x80x9cclamshellxe2x80x9d to open, as urged by the compression spring. The lower edge of the headrest""s contact portion is thus urged toward the occupant""s head.
Significantly, because the contact portion of the headrest advances toward the occupant""s head through rotation about its upper edge, the inclination of the headrest""s engaging surface similarly changes during such an advance, with the degree of advancement of any particular point on the headrest""s engaging surface being inversely related to its relative height above the seat cushion. The uppermost part of the headrest""s contact portion (proximate to the pivot axis) remains essentially stationary as the contact portion advances upon release of the tensioned Bowden cable.
In yet another prior art approach, U.S. Pat. No. 6,082,817 teaches a multi-link system for supporting the contact portion of the headrest relative to a fixed base portion. Upon the tensioning of a Bowden cable, for example, using a pyrotechnic charge, the contact portion moves both forwardly and upwardly as the links rotate about respective, parallel-spaced axis. While the use of multiple links can effect a forward movement of the forward part of the headrest without an attendant change in the engaging surface""s inclination, the relative height of the engaging surface changes during the deployment, thereby presenting the possibility that the contact portion of the headrest will not achieve a desired engagement with the occupant""s head.
It is an object to provide a head restraint or xe2x80x9cheadrestxe2x80x9d for an automotive seat that features an occupant-engaging contact portion that is displaced, in response to a rear collision, to a maximum forward position relative to a backrest-mounted base portion while otherwise maintaining the nominal height and inclination of the contact portion""s occupant-engaging surface.
Another object of the invention is to provide a headrest for an automotive seat whose displaceable, occupant-engaging contact portion becomes locked at or near the maximum forward position in the event of a rear collision of a sufficient magnitude.
It is a further object of the invention to provide a vehicle seat including a movable headrest featuring a simple construction with reliable functioning and simple operability.
Yet another object of the invention is to provide a headrest for an automotive seat whose occupant-engaging contact portion may be selectively displaced, relative to a backrest-mounted base portion, to each of several intermediate forward positions to thereby improve occupant comfort in the absence of a crash condition.
Under the invention, a headrest for a motor vehicle backrest for an occupant seat of a motor vehicle includes a base portion; an occupant-engaging contact portion supported for relative translational movement on the base portion; an articulated spread-lever arrangement linking the base portion and the contact portion and operative to displace the contact portion away from the base portion upon relative rotation of a first link of the arrangement relative to a second link of the arrangement; and a tension spring extending between the contact portion and the base portion and urging the contact portion toward the base portion, whereby rotation of the first link of the arrangement relative to the second link of the arrangement causes a translation of the contact portion relative to the base portion. While the invention contemplates any suitable mechanism for ensuring only relative translational movement of the contact portion away from the base portion, in a preferred embodiment, the base portion includes a track that may be integrally formed, and the contact portion is translated within the track of the base portion.
While the invention contemplates any suitable mechanical or electro-mechanical actuator for effecting the deployment of the contact portion away from the base portion of the headrest, in an exemplary embodiment, a mechanical actuator includes a pressure plate disposed within the backrest frame that tensions a Bowden cable in response to an application of the occupant""s body against the backrest. In one exemplary actuator, rearward movement of the pressure plate relative to the backrest frame imparts rotary motion to an eccentric cam to thereby tension the Bowden cable. Another exemplary actuator employs a lever arm which laterally urges the Bowden cable into a corresponding pocket of an adjacent receiving block so as to similarly tension the Bowden cable. One or more tension springs extending between the contact portion and the base portion urge the contact portion toward the base portion. The tension springs further advantageously work to eliminate any associated rattling.
In accordance with another feature of the invention, the headrest includes an overcenter position for the spread-lever arrangement by which the contact portion becomes locked in or near the maximum forward position once the contact portion has been maximally advanced, for example, in response to a rear collision of sufficient magnitude.
In accordance with another feature of the invention, the use of a tensioning Bowden cable and resisting tension springs advantageously permits a partial relative deployment of the contact portion of the headrest, for example, based upon a detected severity of a rear impact or, alternatively, responsive to a secondary input such as a relative height adjustment of the base portion on the seat backrest. Because such a partial deployment will not cause the spred-lever arrangement to lock in an over-center position, a partially-deployed contact portion can advantageously thereafter be returned, under the control of the Bowden cable, to a position proximate to the base portion.
Thus, in another exemplary design, the power adjustment of the relative height of the headrest atop the backrest frame provides a correlative forward displacement of the contact portion relative to the base portion. In such a case, the invention contemplates a partial deployment of the contact portion relative to the base portion in response to such height adjustment, either by virtue of a direct manipulation of the tension applied by the Bowden cable, or through use of a secondary actuating cable.
Other advantages, features, and benefits of the invention will be readily apparent from the following detailed description of a preferred embodiment, when taken in connection with the accompanying Drawings.